<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
  </head>
  <body>
    <script type="text/javascript">
    function tulin(say){
    switch (say) {
      case '云':
      console.log('乌云密布')
        break;
        case '云':
        console.log('乌布')
          break;

      default:

    }
    }
    tulin('云')
    </script>
  </body>
</html>
